3.2.5 Transition metals Flashcards
what are the physical and chemical properties of transition metals?
- formation of coloured ions
- variable oxidation state
- catalytic activity
- can form complexes
what is meant by ‘ligand’?
a molecule or ion that forms a co-ordinate
bond with a transition metal by donating a pair of
electrons
what is meant by a ‘complex’?
central metal atom or ion surrounded by
ligands
what is meant by ‘co-ordination number’?
the number of co-ordinate bonds to
the central metal atom or ion
what is meant by a ‘Lewis acid’ and does the metal ion or the ligand act as one?
- electron pair acceptor
- metal ion
what is meant by a ‘Lewis base’ and does the metal ion or the ligand act as one?
- electron pair donor
- ligand
what is meant by a ‘bidentate ligand’ and give an example?
- they can form 2 co-ordinate bonds
- e.g. ethane-1,2-diamine; C2O4
(2–) [oxalate]
what is meant by a ‘multidentate ligand’ and give an example?
- can form 3 or more co-ordinate bonds
- e.g. EDTA (4-)
what makes Cl- different to NH3 and H2O as ligands?
- NH3 and H2O are similar in size and uncharged, so the coordination number does not change when undergoing ligand substitution
- Cl- is much larger so the coordination number changes
what is ‘Haem’, how is it formed and what is it used for?
- iron(II) complex with a multidentate ligand
- oxygen forms a co-ordinate bond to Fe(II) in
haemoglobin, enabling oxygen to be transported in the
blood
why is carbon monoxide toxic to humans?
it replaces oxygen co-ordinately bonded to Fe(II) in haemoglobinm, preventing it from being transported in the blood
what is meant by the ‘chelate effect’?
- when bidentate and multidentate ligands replace monodentate
ligands from complexes.
what does the chelate effect do?
- positive entropy change in ligand substitution is favourable as a more stable complex is formed, meaning it’s better to have more moles on the right
- greater entopy change = more negative ΔG = more favourable
- this is achieved through the chelate effect
why is the enthalpy change for ligand substitution so small?
the bonds being formed are very similar to the bonds being broken
what is the criteria to undergo cis/trans geometric isomerism?
- must be octahedral with 2 types of ligands (6 monodentate ligands); e.g. [Cu(H2O)4(OH)2)]
- square planar (4 monodentate ligands; 2 of each type)
what would a cis geometric isomerism look like e.g. [Cu(NH3)4Cl2]
the Cl group would be next to each other (90 degrees apart)
what would a trans geometric isomerism look like e.g. [Cu(NH3)4Cl2]
the Cl would be opposite each other (180 degrees apart)
what is the compound for cisplatin and how would you draw it and transplatin?
- Pt(NH3)2Cl2
- cisplatin -> Pt in the centre; NH3 and Cl will be on opposite sides (square planar shape)
- transplatin -> NH3 and Cl on same side
what is the criteria to undergo optical isomerism?
- non-superimposable mirror images
- must be octahedral with 3 bidentate ligands
react [Cu(H2O)6]2+ (aq) with NH3 (aq)
[Cu(H2O)6]2+ (aq) + 4NH3 (aq) ⇌ [Cu(H2O)2(NH3)4]2+ (aq) + 4H2O (l)
what colour is [Cu(H2O)6]2+ (aq)
blue solution
what colour is [Cu(H2O)2(NH3)4]2+ (aq)
deep blue solution
describe what happens when you react [Cu(H2O)6]2+ (aq) with NH3 (aq) and why this occurs
- change in colour because there is a change in ligand
- no change in coordination number or shape because the ligands H2O and NH3 are neutral and similar in size
react [Cu(H2O)6]2+ (aq) with Cl- (aq)
[Cu(H2O)6]2+ (aq) + 4Cl- (aq) ⇌ [CuCl4]2- (aq) + 6H2O (l)
describe what happens when [Cu(H2O)6]2+ (aq) reacts with 4Cl- (aq) and why this happens
- change in colour due to change in ligand
- change in coord. no and shape because 4 chloride ions replace 6 water molecules (chloride ions are bigger than H2O)
what colour is [CuCl4]2+
yellow solution
react [Co(H2O)6]2+ with NH3
[Co(H2O)6]2+ (aq) + 6NH3 (aq) ⇌ [Co(NH3)6]2+ (aq) + 6H2O (l)
what colour is [Co(H2O)6]2+
pink solution
what colour is [Co(NH3)6]2+
straw coloured solution
what is meant by a homogeneous + hetergeneous catalyst
- homo - same phase as the reactant
- hetero - diff. phase to the reactants
process of a catalyst
- reactants adsorb onto the surface/active site of the catalyst
- bonds weaken/reaction takes place
- products desorb from the surface
what happens after reactants are adsorbed?
they are desorbed (ie they leave the surface)
what happens (in regards of adsorption and desorption) if the catalyst is too strong or weak? give an example of a strong and a weak catalyst.
too strong (e.g. tungsten) -> reactants cannot move around the surface; this prevents them from desorbing
too weak (e.g. silver) -> reactants cannot get adsorbed
how does catalyst poisoning cause the rate of reaction to stay the same?
reaction impurities -> blocks the active site -> prevents adsorption -> bonds of the molecules stay strong -> harder to break -> catalyst has no event on RoR
what happens to costs when there are impurities in the reaction?
increase in chemical production costs because the catalyst needs to be replaced or cleaned regularly
how do you calculate the energy absorbed by the electrons and what are the units
ΔE = hv = hc / λ
- ΔE = energy gap (J)
- h = Planck’s constant (6.63 x10(-34))
- v = frequency of light absorbed (Hz)
- c = speed of light (3x10(8))
- λ = wavelength of light (m)
what are the colours of vanadium at different oxidation states?
- V(2+) - violet
- V(3+) - green
- VO(2+) - blue
- VO2(+) - yellow
explain why an aqueous solution containing [Fe(H2O)6]
3+ ions has a lower pH than one containing [Fe(H2O)6]2+ ions. (3 marks)
- Fe3+ has a greater charge density/smaller than Fe2+
- Fe3+ is more polarising/polarises water molecules more
- therefore more O-H bonds break/are weakened
Explain why complexes formed from transition metal ions are coloured.
(3 marks)
- absorb (some) frequencies of (visible) light
- to promote/excite electrons in d-orbitals
- remaining/complementary /frequencies/colours/energies of (visible) light are reflected/transmitted to give the colour seen
